Normothermic heater covering for tissue treatment

ABSTRACT

An apparatus applies heat to tissue from a level that does not contact the tissue in order to elevate the temperature of the tissue being treated toward normothermia. The, apparatus has a ring that surrounds, but does not contact the tissue to be treated. This ring has a layer out of contact with the tissue to be treated at which a heater is located. The apparatus may be attached to the skin of a person so that the ring and the layer form a treatment volume which does not contact the tissue to be treated. The heater, supported at the layer, is held near the tissue to be treated, out of contact with the tissue. The heater may be an active heater, or an inactive, reflective heater. If active, the apparatus may include a programmable active heater controller. One form of an active heater is an electrical resistant filament which may have various geometric shapes in order to provide versatility in application of heat to the tissue to be treated.

CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/491,716, filed Jan. 27, 2000, titled NORMOTHERMIC HEATER WOUNDCOVERING, now U.S. Pat. No. 6,217,535, which is a continuation of U.S.patent application Ser. No. 09/271,823, filed Mar. 18, 1999, now Pat.No. 6,045,518, which is a continuation of U.S. patent application Ser.No. 08/785,794 filed Jan. 21, 1997, now U.S. Pat. No. 5,986,163, whichis a continuation-in-part of U.S. patent application Ser. No.08/356,325, filed Feb. 21, 1995, titled WOUND COVERING, now abandoned,which is a 35 USC §371 application of PCT International application Ser.No. PCT/US93/05876, filed Jun. 18, 1993, titled WOUND COVERING, which isa continuation-in-part of, and claims priority from U.S. patentapplication Ser. No. 07,900,656, filed Jun. 19, 1992, now abandoned.

FIELD OF THE INVENTION

This invention relates to a covering for heat treatment of tissue and,in particular, covers having a substantial portion of the cover innon-contact with the tissue and capable of delivering heat to thetissue. The covering preferably controls the temperature, humidity andother aspects of the environment at the tissue.

BACKGROUND OF THE INVENTION

Wounds in general, as used in this context, are breaks in the integrityof the skin of a patient. Wounds may occur by several differentmechanisms. One such mechanism is through mechanical traumatic meanssuch as cuts, tears, and abrasions. There are many instruments ofcasualty for mechanical wounds, including a kitchen bread knife, brokenglass, gravel on the street, or a surgeon's scalpel. A differentmechanism cause for mechanical wounds is the variable combination ofheat and pressure, when the heat alone is insufficient to cause anoutright burn. Such wounds that result are collectively referred to aspressure sores, decubitus ulcers, or bed sores, and reflect a mechanicalinjury that is more chronic in nature.

Another type of mechanism causing a wound is vascular in origin, eitherarterial or venous. The blood flow through the affected region isaltered sufficiently to cause secondary weakening of the tissues whicheventually disrupt, forming a wound. In the case of arterial causes, theprimary difficulty is getting oxygenated blood to the affected area. Forvenous causes, the primary difficulty is fluid congestion to theaffected area which backs up, decreasing the flow of oxygenated blood.Because these wounds represent the skin manifestation of otherunderlying chronic disease processes, for example, atheroscleroticvascular disease, congestive heart failure, and diabetes, these vascularinjuries also are chronic in nature, forming wounds with ulceratedbases.

Traditional wound coverings, such as bandages, are used to mechanicallycover and assist in closing wounds. Such bandages typically cover thewound in direct contact with the wound. This may be acceptable foracute, non-infected traumatic wounds, but it must be kept in mind thatdirect bandage contact with a wound can interfere with the healingprocess. This interference is particularly prevalent for chroniculcerated wounds because of the repeated mechanical impact andinteraction of the bandage with the fragile, pressure sensitive tissueswithin the wound.

The benefits of application of heat to a wound are known, and documentedbenefits include: increased cutaneous and subcutaneous blood flow;increased oxygen partial pressure at the wound site; and increasedimmune system functions, both humoral and cell mediated, includingincreased migration of white blood cells and fibroblasts to the site.

However, heat therapy for the treatment of wounds, either infected orclean, has been difficult to achieve in practice. For instance, heatinglamps have been used, but these results in drying of wounds, and in somecases, even burning tissue from the high heat. Due to these and otherdifficulties, and since most acute wounds usually heal over time,physicians no longer consider the application of heat to the wound aspart of the treatment process. The thinking among medical personnel isthat any interference in a natural process should be minimized until itis probable that the natural process is going to fail. Additionally, theavailability of antibiotics for use in association with infected woundshas taken precedence over other therapies for the treatment of chronicwounds and topical infections.

In French patent number 1,527,887 issued Apr. 29, 1968 to Veilhan thereis disclosed a covering with rigid oval dome, its edge resting directlyon the patient's skin. One aspect of the Veilhan wound protector is asingle oval heating element resting on the outer surface of the rigiddome, positioned at the periphery of the rigid dome. Veilhan does notdiscuss the heating aspect other than to state that it is a component.

The benefits of controlling other environmental parameters around thewound site are not as well known. Controlling the humidity at the woundsite and the benefits of isolating the wound have not been extensivelystudied and documented.

While the benefit of applying heat to wounds is generally known, themanner of how the heat should be used or applied is not known.Historically, heat was applied at higher temperatures with the goal ofmaking the wound hyperthermic. These higher temperatures often resultedin increasing tissue damage rather than their intended purpose of woundtherapy and healing. There is a need for appropriate wound caremanagement incorporating a heating regimen that is conducive to woundhealing, yet safe and cost effective.

SUMMARY OF THE INVENTION

The present invention disclosed herein approaches the treatment ofwounds with heat based on an understanding of physiology. The normalcore temperature of the human body, what will be defined herein forpurposes of this disclosure, is 37° C.±1° C. (36°-38°C.), whichrepresents the normal range of core temperatures for the humanpopulation. For purposes of discussion and this disclosure, normal coretemperature is the same as normothermia. Depending on the environmentalambient temperature, insulative clothing and location on the body, skintemperature typically ranges between about 32° C. and about 37° C. Froma physiologic point of view, a 32° C. skin temperature of the healthydistal leg is moderate hypothermia. The skin of the distal leg of apatient with vascular insufficiency may be as low as 25°C. under normalconditions, which is severe hypothermia.

A fundamental physiologic premise is that all cellular physiologicfunctions, biochemical and enzymatic reactions in the human body areoptimal at normal body core temperature. The importance of this premiseis seen in how tightly core temperature is regulated. Normalthermoregulatory responses occur when the core temperature changes aslittle as ±0.1° C. However, the skin, as noted above, is usuallyhypothermic to varying degrees. For example, the skin of the torso isusually only slightly hypothermic, whereas the skin of the lower legs isalways hypothermic. Consequently, wounds and ulcers of the skin,regardless of location, are usually hypothermic. This skin hypothermiaslows cellular functions and biochemical reactions, inhibiting woundhealing.

The effects of hypothermia on healing are well known. A number ofregulatory systems within a human are affected, such as the immunesystem and coagulation, with both platelet function as well as theclotting cascade affected. Patients with hypothermic wounds experiencemore infections which are more difficult to treat, have increasedbleeding times and have been shown to require more transfusions ofblood. All of these complications increase morbidity and the cost ofpatient care and, to a lesser extent, increase the likelihood ofmortality.

One purpose of the present invention is to raise the wound tissue and/orperiwound tissue temperatures toward normothermia to promote a moreoptimal healing environment. The present invention is not a “heatingtherapy”, per se, where it is the intent of “heating therapy” to heatthe tissue above normothermia to hyperthermia levels. Rather, thepresent invention is intended to bring the wound and periwound tissuestoward normothermia without exceeding normothermia.

The medical community has not historically considered normothermicheating to be therapeutic. Many physicians feel that hypothermia isprotective and, therefore, desirable. Studies with the present inventionwould indicate that this widely held belief that hypothermia is at leastbenign or possibly beneficial is incorrect with regard to wound healing.

The present invention is a wound covering for application to a selectedtreatment area of a patient's body that includes, at least as a portionof the selected treatment area, a selected wound area. The selectedtreatment area may also include a portion of the area immediatelyproximate to the wound area referred to as the periwound area. The woundcovering comprises a heater suitable for providing heat to the selectedtreatment area, an attachment for attaching the heater in a non-contactposition over the selected treatment area, and a heater controller,connected to the heater and including a power source for the heater, forcontrolling the temperature of the heater in a temperature range fromabove ambient temperature to about 38° C. Ambient temperature is thattemperature of the environment immediately around the selected treatmentarea not a portion of the patient's body, i.e., the bed, the air in theroom, the patient's clothing, etc.

The heater is selectable from among several types of heat sources suchas warmed gases directed over the selected treatment area and electricalheater arrays placed proximate the selected treatment area. Electricalheater arrays are adaptable for construction into a layer of variableproportion and geometry or as a point source. The present inventionanticipates the ability to provide several different sizes and geometricconfigurations for the heater. The present invention is flexible inbeing able to provide uniform heating over the entire selected treatmentarea or provide a non-uniform heating distribution over selectedportions of the selected treatment area. Alternate heat sourceembodiments could include warm water pads, exothermic chemical heatingpads, phase-change salt pads, or other heat source materials.

The present invention anticipates that the controller is able to controlboth the temperature and the duration of the application of heat. Thiscontrol may extend from manual to fully automatic. Manual controlanticipates the controller maintaining the heater temperature at anoperator-selected temperature for as long as the operator leaves theheater on. More automatic modes provide the operator an ability to enterduty cycles, to set operating temperatures, as well as to define therapycycles and therapeutic sequences. As used herein, a duty cycle is asingle on cycle when heating of the heater is occurring, measured fromthe beginning of the on cycle to the end of that on cycle. A heatercycle is a single complete on/off cycle measured from the beginning of aduty cycle to the beginning of the next duty cycle. Consequently, a dutycycle may also be represented in a percentage of, or as a ratio of thetime on over the time off. A plurality of heater cycles are used tomaintain heater temperature around a selectable temperature set pointduring a therapy cycle which is defined as an “on” period, composed of aplurality of heater cycles, and an “off” period equivalent to the heaterremaining off for an extended period of time. A therapeutic sequence, asused herein, is a longer period of time usually involving a plurality oftherapy cycles spread out over an extended period of time, the mostobvious being a day in length. The present invention anticipates the useof any period of time as a therapeutic sequence and involving one, ormore than one therapy cycles.

The present invention also anticipates programmability for a number ofmodalities including peak heater temperature for a duty cycle and/ortherapy cycle, average heater temperature for a duty cycle and/ortherapy cycle, minimum heater temperature for a heater cycle and/ortherapy cycle, ratio of duty cycle, length of therapy cycle, number ofduty cycles within a therapy cycle, and number of therapy cycles in atherapeutic sequence. Different duty cycles within a therapy cycle maybe programmed to have different peak heater temperatures and/or heatercycles may have average heater temperatures over that therapy cycle.Different therapy cycles within a therapeutic sequence may be programmedto have different peak heater temperatures and/or average heatertemperatures over each therapy cycle. The wound covering control isoperator-programmable or may have preprogrammed duty cycles, therapycycles, and therapeutic sequences selectable by the operator.

A preferred form of the wound covering includes an attachment as aperipheral sealing ring which, in use, completely surrounds the area ofthe wound and periwound, i.e., the selected treatment area. The uppersurface of the peripheral sealing ring is spanned by a continuous layerwhich is preferably transparent and substantially impermeable, althoughthe present invention also anticipates the use of a gas permeable layersuitable for some applications. Once in position, the sealing ring andthe layer define a wound treatment volume which surrounds the wound.Additionally, the layer spanning the peripheral sealing ring may besealed about the periphery of the sealing ring and act as a barrierlayer over the wound treatment volume. Optionally, the heater may beincorporated into the barrier layer or the barrier layer may beincorporated into the heater. An adhesive and a suitable release lineris applied to the lower surface of the peripheral sealing ring tofacilitate the application of the wound covering to the patient's skin.

The barrier layer may include a pocket adapted to receive an activeheater. An alternate form of the invention provides for the transport ofheated air from a remote heater source to the wound treatment volume. Inthe active heater embodiments a thermostat and/or a pressure-activatedswitch may be used to control the heating effects of the heater.Passively heated embodiments are contemplated as well. These passiveversions of the device include the use of thermally insulating coveringswhich retain body heat within the treatment volume. These reflectors orinsulators may be placed in a pocket formed in the barrier layer. Eachof these heated embodiments promote wound healing by maintaining thewound site at a generally elevated, but controlled, temperature.

In general, the peripheral sealing ring is made from an absorbentmaterial which may act as a reservoir to retain and/or dispense moistureinto the treatment volume increasing the humidity at the wound site. Thereservoir may also contain and deliver medicaments and the like topromote healing.

The present invention is designed to elevate the temperature of thehypothermic skin and subcutaneous tissue of the selected treatment areato a temperature which is close to normothermia. The purpose of thisdevice is to create within the wound and periwound tissues of theselected treatment area a more normal physiologic condition,specifically a more normothermic condition, which is conducive to betterwound healing. The present invention anticipates the use of an activeheater, but the role of the heater can better described as “guarding”against heat loss by providing a heat source to counteract the effectsof heat loss.

The concept of a guard heater is straightforward. The guard heater isheated to approximately the same temperature as the adjacent heatedbody. Since heat must flow down a temperature gradient, it can only belost to a cooler surface. The guard heater is not cooler than theadjacent body and, therefore, cannot accept heat from the adjacent body.The normal temperature gradient for tissue goes from about 37° C. deepin the body's core down to about 32° C. at the skin's surface. With aguard heater in place, heat loss directly from the wound and periwoundtissue surfaces is markedly diminished. This decrease in local heat lossprovides for the zone of 37° C. core temperature to move outward towardthe skin, narrowing the gradient from core temperature to surfacetemperature as the zone of core temperature approaches the surface inthe area of the guard heater. The guard heater behaves very much like aperfect insulator, providing a circumstance suitable for warming of thewound with heat flowing from the core. The guard heater of the presentinvention has an additional advantage over neat-perfect passiveinsulation in that near-perfect insulation would require the use ofseveral inches of bulky insulating material. Such bulkiness in a wounddressing is not practical for proper wound care.

The “guard” heater of the present invention, for example in use onwounds below the knee where vascular insufficiency may occur, operatesfrom the above ambient temperature to 38° C., which includes the rangeof “normothermia”. Obviously, because of the thermal mass of the leg,the blood flow through the leg and inherent inefficiencies of heattransfer, the resulting wound and periwound tissue temperatures usuallyremain less than the operating temperature of the “guard” heater, andprobably less than the patient's core temperature.

In contrast, typical local heating therapy (e.g. hot water bottles, hotwater pads, chemical warmers, infrared lamps) deliver temperaturesgreater than 46° C. to the skin. The goal of traditional heating therapyis to heat the tissue above normal, to hyperthermic temperatures.

The present invention differs from infrared lamps in two ways. First,the present invention includes a dome over the wound that is relativelyimpermeable to water vapor transmission. After application of thebandage, moisture from the intact skin or wound evaporates, and airwithin the dome quickly reaches 100% relative humidity. The interior ofthe present invention is now warm and humid. For example, a 2.5 squareinch bandage at 28°C. requires only 0.0014 g of water to reachsaturation. When the air is thus saturated, no further evaporation canoccur and, therefore, no drying of the wound can occur. This equilibriumwill be maintained as long as the bandage is attached to the patient.

When heat is provided by the preferred embodiment of the presentinvention, the absolute amount of water needed to reach 100% relativehumidity is slightly increased since warm air has a greater capacity forholding moisture. However, the air within the dome of the bandage stillreaches water vapor saturation very quickly, and no further evaporationoccurs. For example, a 2.5 square inch bandage of the present inventionat 38° C. requires only 0.0024 g of water to reach saturation. Excessmoisture is absorbed by the foam ring, but still is retained within thebandage. The enclosed dome design maintains 100% humidity over the woundwhich also prevents evaporation due to the heat. As long as the humidityis retained within the bandage, heating therapy could theoretically becontinued indefinitely without causing the wound to dry. In contrast,when using infrared lamps, the wounds are open and exposed to theenvironment. The result is excessive drying of the wound, increasingtissue damage.

Secondly, the present invention operates at low temperatures, from aboveambient to about 38° C. This causes only minimal heating of the skin. Incontrast, infrared lamps operate at temperatures in excess of 200° C.These lamps heat the wound to hyperthermic temperatures which can causethermal damage to the tissue of the wound.

At the low (normothermic) operating temperatures of the presentinvention, the heat transfer to the skin is minimal. The low wattageheater, the inefficiencies of the heat transfer into the tissue, thethermal mass of the tissue and the blood flow (even if markedlyreduced), all prevent the wound temperature from reaching the heatertemperature. Hypothermic wound tissue is warmed as a result of“migration” of the body's core temperature zone toward the local woundarea.

The following data document the tissue temperature resulting from a 38°C. heater of the present invention on:

Average Maximum Normally perfused human skin 36° C. 36° C.Arterial/diabetic foot ulcers 32° C. 35° C. Venous/arterial leg/footulcers 33° C. 35° C. Non-perfused human model 35° C. 35° C.

When warmed with a 38° C. heater, wounds on poorly perfused legs reachstable average temperatures of 32-33° C. In contrast, normally perfusedskin reaches 36° C. It is important to note that these data arecontradictory to the assumption that poorly perfused tissue would reacha higher temperature than normally perfused tissue. This resultsubstantiates the physiologic finding that the “migration” of the coretemperature zone toward the local wound zone, decreasing the gradientdifference between the core and surface temperatures, is the cause forthe observed increased wound temperatures. Core temperature regulationis heavily dependent on perfusion, and migration of the core temperaturezone is also heavily dependent on perfusion. At no point in time did thepoorly perfused tissue reach normothermia. Poorly perfused legs arecolder than normally perfused legs, and, thus, poorly perfused legsconstitute a substantially deeper heat-sink.

A wound-healing pilot study is under way, studying patients with chronicarterial and/or venous ulcers of the lower leg. These patients havesuffered from these ulcers for many months and, in some cases, evenyears, despite aggressive medical and surgical therapy. Of 29 patientsenrolled, 24 have completed the study protocol or are still beingtreated. Of these 24 patient's, 29% are completely healed, and 38% showa significant reduction of the wound size with 2-5 weeks of receivingtherapy with the present invention.

A known consequence of restoring normothermia to tissues is to inducesome degree of vasodilatation which increases local blood flow.Preliminary data collected during trials of the present invention,studying the effects of the present invention on normal subjects and onwound healing, has borne this out. An added effect has been to increasethe partial pressure of oxygen in the subcutaneous tissues (P_(sq)O₂),which is an indirect indicator of the status of the tissue. The higherthe P_(sq)O₂, the greater the likelihood the tissue will benefit andimprove the healing process. The results of some of these studies arepresented in Tables 1-4.

In conducting the studies presented in Tables 1-4, a wound coveringaccording to the present invention is placed over the skin. Thetemperature of the subcutaneous tissue is then measured over time. From−60 minutes to the 0 minute mark, the heater is off in order to obtain abaseline temperature. At the 0 minute mark the heater is activated andits temperature kept constant over the next 120 minutes when it isturned off. Temperature measurements were taken during this 120 minuteperiod and for an additional 180 minutes after turning the heater off.As shown in Table 1, with activation of the heater to 38° C., thesubcutaneous tissue temperature rapidly rose from about 34.3° C. toabout 36° C. over the first 30 minutes. The temperature of thesubcutaneous tissue continued to slowly raise over the next 90 minutesto a temperature of about 36.7° C. After turning the heater off, thetemperature of the subcutaneous tissue fell to about 35.9° C. and heldthis temperature fairly uniformly for at least the next 120 minutes.

Table 2 presents the skin temperature data collected from within thewound cover of the present invention for the same periods as those inTable 1. The general curve shape is similar to the subcutaneous tissuetemperature curve. The baseline temperature at the 0 minute mark wasabout 33.5° C. After turning the heater on to 38° C., the skintemperature rose rapidly to about 35.8° C. in the first 30 minutes, thenslowly rose to about 36.2° C. by the end of the 120 minute heatingperiod. After turning the heater off, the skin temperature fell to about35° C. and held there for at least the next two hours.

Table 3 represents laser Doppler data collected from the tissue duringthe experiments and correlates to blood flow through the local areabeing treated with heat. The baseline flow is approximately 80 ml/100g/min and rises to about 200 ml/100 g/min at its peak, half way throughthe heating period. The flow “normalizes” back to baseline during thelast half of the heating period and remains at about baseline for theremainder of the measuring period.

The change in P_(sq)O₂ is followed in Table 4. The baseline P_(sq)O₂ isabout 75 when heating begins and rises steadily to about 130 by the endof the heating period. The P_(sq)O₂ remains at this level for theremainder of the measuring period despite the lack of heating for thelast 180 minutes. The added benefit of increased P_(sq)O₂ by heatingcontinues well into the period of time after active heating has ceased.Wounds will continue to benefit from the effects of heating forsubstantial periods of time after the heating is turned off. Theconsequences of this study with the present invention is that theheating need not be constant, but deliverable over a heater therapycycle or cycles that may nor may not be part of a larger therapeuticsequence.

Out initial human clinical data shows that the beneficial effects ofheating on blood flow and P_(sq)O₂ last at least one hour longer thanthe actual duration of heat application. Further, we have noted thatcycled heating seems to be more effective for wound healing thancontinuous heating. Therefore, the data recommends cycling the heater ina therapy cycle (e.g. 1 hour “on” and 1 hour “off”) for a total heatingtime of 2-8 hours per day as a therapeutic sequence.

None of the 29 patients with compromised circulation treated to datehave shown any indication of skin damage due to 38° C. heat.Furthermore, none of these wounds have exceeded 35° C. tissuetemperature, with an average wound temperature of 32-33° C. The presentinvention raises the wound temperature toward normothermia, but even ona poorly perfused leg, the tissue does not reach normothermia.

Accordingly, the invention concerns an apparatus for applying heat totissue from a level that does not contact the tissue in order to elevatethe temperature of the tissue being treated toward normothermia. Thisobjective is accomplished by means of an apparatus having a ring thatsurrounds, but does not contact the tissue to be treated. This ring hasa layer out of contact with the tissue to be treated at which a heateris located. The apparatus may be attached to the skin of a person sothat the ring and the layer form a treatment volume which does notcontact the tissue to be treated. The heater, supported at the layer, isheld near the tissue to be treated, out of contact with the tissue. Theheater may be an active heater, or an inactive, reflective heater. Ifactive, the apparatus may include a programmable active heatercontroller. One form of an active heater is an electrical resistantfilament which may have various geometric shapes in order to provideversatility in application of heat to the tissue to be treated.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative but not limiting embodiments of the invention are shown inthe attached drawings. Throughout the several figures like referencenumerals refer to identical structure throughout, in which:

FIG. 1A is an exploded view of a wound covering according to the presentinvention;

FIG. 1B illustrates an assembled view of the wound covering of FIG. 1A;

FIG. 2A is a view of an alternate wound covering;

FIG. 2B is a view of an alternate wound covering of FIG. 2A with passiveheating card inserted in the wound covering;

FIG. 3A is an exploded view of an additional alternate wound covering;

FIG. 3B is an assembled view of the wound covering of FIG. 3A;

FIG. 4 is a side elevation view of a wound covering;

FIG. 5 is an enlarged top plan view of a wound covering;

FIG. 6 is an enlarged sectional view taken along line 6—6 of FIG. 5;

FIG. 7 is a bottom view of the wound covering of FIG. 4;

FIG. 8A is an exploded view of an alternate wound covering;

FIG. 8B is an assembly view showing the air flow through the woundcovering;

FIG. 9A is a perspective view of an alternate wound covering;

FIG. 9B is a side view of the wound covering of FIG. 9A;

FIG. 10 is a perspective view of an alternate wound covering;

FIG. 11A is a perspective view of an alternate wound covering;

FIG. 11B is a side elevational view of the wound covering of FIG. 11A;

FIG. 11C is a view of the wound covering of FIG. 11A;

FIG. 12 is a perspective view of an alternate connector apparatus forthe wound covering;

FIG. 13A is an alternate connector arrangement for the wound covering;

FIG. 13B is a side sectional view of the wound covering of FIG. 13A;

FIG. 14 is a view of a rigid connector for engagement with a woundcovering;

FIG. 15 is an alternate fluid inlet line for the wound covering;

FIG. 16A is a view of a two ply barrier layer wound covering;

FIG. 16B is a side elevational view of the wound covering of FIG. 16A;

FIG. 17 is an alternate wound covering;

FIG. 18A is an alternate wound covering;

FIG. 18B is a side sectional view of the wound covering of FIG. 18A;

FIG. 19 is a side elevational view of an alternate wound covering

FIG. 20 is a schematic diagram of an embodiment of the presentinvention; and

FIG. 21A is a schematic representation of an alternate embodiment of theheater array distribution shown in FIG. 20;

FIG. 21B is a schematic representation of an alternate embodiment of theheater array distribution shown in FIGS. 20 and 21A;

FIG. 21C is a schematic representation of an alternate embodiment of theheater array distribution shown in FIGS. 20, 21A, and 21B;

FIG. 21D is a schematic representation of an alternate embodiment of theheater array distribution shown in FIGS. 20, 21A, 21B, and 21C;

FIG. 22 is a graphical representative sample of an operational schemefor an embodiment of the present invention, such as the embodiment shownin FIG. 20;

FIG. 23 is a graphical representative sample of an additionaloperational scheme for an embodiment of the present invention, such asthe embodiment shown in FIG. 20 using the scheme depicted in FIG. 22;and

FIG. 24 is a graphical representative sample of another additionaloperational scheme for an embodiment of the present invention, such asthe embodiment shown in FIG. 20 using the schemes depicted in FIGS. 22and 23.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a non-contact wound covering forcontrolling the local environment at wound site on a patient. A woundsite includes those portions of the patient's skin obviously definableas the wound area and the immediately adjacent periwound area as theselected treatment area of the wound site. The wound covering protectsthe wound from contamination by materials from the outside environmentand also prevents the wound site from shedding contaminants into thelocal environment of the patient, i.e. the hospital room. The treatmentvolume formed proximate the wound site can be controlled to create anoptimal healing environment. The word “wound” as used herein refersgenerically to surgical incisions, ulcers, or other lesions or breaks inthe skin.

First, a substantially vertical wall is provided to encircle theselected treatment area on the surface of the patient's skin. Thisvertical wall provides an upper surface to support a layer spanning thisstructure above the level of the wound and a lower surface suitable forattachment to the patient's skin. This structure is referred tothroughout as an attachment or a peripheral sealing ring. Together theseelements form a wound treatment volume between the layer and the surfaceof the selected treatment area. The fact that the layer does not contactthe wound itself promotes healing by minimizing mechanical stresses onthe tissues. The lower surface suitable for attaching to the skin mayinclude an adhesive and a complimentary release liner assembly tofacilitate the attachment of the wound covering to the skin of thepatient. The present invention anticipates using a heater such that thelayer may comprise the heater formed as the layer or as a layer whichincludes a heater within some portion of the layer. The layer may alsoinclude functioning as a barrier layer completely enclosing the woundtreatment volume.

In accordance with the present invention, the climate within the woundtreatment volume may be controlled. Typically the temperature, humidity,and gas composition, for example adding oxygen, nitric oxide or ozone,are controlled. Also, aerosolized medications or compounds may bereleased into this volume as well. The above list is exemplary of theclimate controls which may promote healing of the wound, and is notintended to limit the scope of the present invention. It will beunderstood by those skilled in the art that numerous other climatefactors can be controlled within the treatment volume of the presentwound covering system without departing from the scope of the invention.

FIG. 1A illustrates an exploded view of a wound covering 50. In thisembodiment, a peripheral sealing ring 52 is substantially square inoutline. Peripheral sealing ring 52 is intended to be attached touninjured skin surrounding a selected treatment area 54 using anadhesive 56. In this embodiment, a layer of adhesive hydrogel is shownas the adhesive 56. Additionally, peripheral sealing ring 52 ispreferably constructed of an open cell hydrophilic foam plastic having asealed outer surface 58 which isolates the wound from the environment.The peripheral sealing ring is fabricated from a material which mayconform to the curved surface of the patient's body. An inner surface 60of the sealing ring 52 is preferably porous or absorbent so that it canform a reservoir to contain and release moisture or water vapor into theair within a treatment volume 62 to create a high humidity environmentif desired. Additionally, the hydrophilic absorbent nature of peripheralsealing ring 52 absorbs fluids and blood weeping from the wound.

A layer 64 is preferably attached to an upper surface 66 of peripheralsealing ring 52 as a barrier layer to seal treatment volume 62. Layer 64is preferably constructed of a flexible synthetic polymeric film, suchas polyethylene, polyvinyl chloride, polyurethane, or polypropylene.Additionally, other polymeric films, natural and semi-synthetic, thatare suitable for use in medical applications such as cellulose andcellulose acetate, may be used. A wound tracing grid 68, alsoconstructed of a substantially clear flexible material, may optionallybe used as, or attached to, layer 64 to facilitate wound care managementso that the physician can drawn an outline of the wound as an aid totracking to healing process of the wound. The wound tracing gridpreferably contains a labeling area 70 for identifying the patient, datewhen the wound was traced, and other patient medical data.

It will be understood by those skilled in the art that the volume ofperipheral sealing ring 52 will depend on the structural strength of thesupport material and the amount of fluid absorption desired.Additionally, the total area of peripheral sealing ring 52 is dependenton the size of the wound. For example, larger wounds and more flexiblecovers will require a thicker sealing ring so that the center of thecover does not touch the wound.

Upper surface 66 of peripheral sealing ring 52 is preferably sealed byextending barrier layer 64 over the entire area of the upper surface 66as shown in FIGS. 1A and 1B. Adhesive 56 for attaching peripheralsealing ring 52 to uninjured skin surrounding selected treatment area 54may take any form, however, the preferred adhesive is preferably atwo-faced hydrogel which attaches to a lower surface 72 of peripheralsealing ring 52. This adhesive 56 permits the attachment of peripheralsealing ring 52 to the patient's skin. Finally, peripheral sealing ring52 may serve as a reservoir for retaining water or medicaments intreatment volume 62 in order to maintain a high humidity in the airwithin the volume. Water may be added to peripheral sealing ring 52 atany time during treatment.

It will be understood by those skilled in the art that peripheralsealing ring 52 can be supplied in a variety of shapes and sizes toaccommodate various wounds. The shapes may include circles, squares, orrectangles. Although it is preferred to dispense the wound covering as aunitary assembly it should be apparent that individual segments ofperipheral ring material could be assembled into any shape necessary toform a perimeter around the wound area. Likewise, barrier layer 64 andwound tracing grid 68 could be provided in large sheets which may be cutto size and then attached to the peripheral sealing ring.

FIG. 1B is an assembled view of wound covering 50 of FIG. 1A. Todispense the assembled product, a release liner 74 of FIG. 1B is appliedto adhesive 56 in FIG. 1A. Release liner 74 may span the entire lowersurface of the covering to maintain the sterility of treatment volume62. Release liner 74 preferably has a grip tab 76 to facilitate removalof release liner 74 from wound covering 50 immediately prior toapplication of wound covering 50 to the skin of a patient.

FIGS. 2A and 2B illustrate an alternate embodiment of the presentinvention as a wound covering 80 utilizing passive heating of thetreatment volume 62. Because heat is constantly being radiated from thepatient's skin surface, the insulation properties of the trapped airwithin treatment volume 62 will reduce this heat loss. By adding aninfrared reflector 82 over treatment volume 62, the infrared heat fromthe body can be reflected back to the skin for added passive heating.

An edge 84 of wound tracing grid 86 is preferably not attached to thebarrier layer to form an envelope or a pocket 94 between the woundtracing grid 86 and the barrier layer. A piece of reflective foilmaterial 88 may be inserted into pocket 94. A thin layer of insulatingmaterial 90 may be optionally attached to foil layer 88 to enhance heatretention and to provide foil layer 88 with additional resiliency. A tab92 is preferably attached to infrared reflector 82 to allow easyinsertion and removal from pocket 94 and wound covering 80.

FIGS. 3A and 3B illustrate a preferred alternate embodiment of anon-contact wound covering 108 utilizing active heating of a treatmentvolume 112. Wounds may be safely and easily heated utilizing a heaterassembly 100. Heater assembly 100 alternatively comprises apressure-sensitive switch 102, an insulating layer 104, and a foilheater 106.

Pressure-sensitive switch 102 is optionally laminated to the uppersurface of heater assembly 100. The purpose of switch 102 is to shut offpower to foil heater 106 in the event that external pressure is appliedto wound covering 108 with sufficient force to cause foil heater 106 tocontact the skin or wound below. This feature prevents the possibilityof applying heat and pressure to the skin at the same time. Thecombination of heat and pressure is known to cause burns even at lowtemperatures (40° C. because the pressure prevents blood flow in theskin making it susceptible to thermal injury. Pressure-sensitive switch102 preferably covers the entire area of heater assembly 100 so thatpressure applied anywhere to the surface of heater assembly 100 willdeactivate foil heater 106.

It will be understood by those skilled in the art that a variety ofdevices are suitable for use as pressure-sensitive switch 102. Forcesensing resistors, resembling a membrane switch, which change resistanceinversely with applied force are one such example of a pressuresensitive switch. Devices of this type offer the substantial advantageof being low cost, flexible, and durable. A variety of other forcesensing switch devices may be utilized as well.

An alternative safety feature anticipated by the present invention is amonitoring function for detecting dramatic increases in powerutilization by the heater trying to maintain an operating temperature.Under normal operation, the heater is in a non-contact positionproximate the selected treatment area and the heater will have beenprogrammed to operate at a temperature that may be either a straighttemperature value or an averaged value for either a duty cycle, therapycycle or therapeutic sequence. If physical pressure is placed on theheater and it comes into contact with the patient's body, there will bea considerable increase in the rate of heat loss from the heater becauseof the body's greater heat sink capacity. The heater controller wouldsense this drop in temperature and initially adjust either the dutycycle ratio or power output, or both, in an attempt to compensate forthe increase rate of loss. The safety aspect of this monitoring functionwould be to override this increase and turn off the device, thuspreventing heating the tissue while in direct contact with, and underpressure from, the heater.

Heater element 106 is preferably a thin film type resistance heaterwhich is commercially available. Such thin film resistance heatersutilize low voltage, minimizing the electrical risk to the patient andallowing for battery-powered mobility. Foil heater 106 is preferablysized for each wound covering 108. In actual use, foil heater 106 ispreferably provided in sheets with a pair of electrical leads 110 alongone edge. While an electrical resistance heater is the preferredembodiment of the invention, other heating devices are anticipated sucha warm water pads, exothermic chemical heating pads, and phase-changesalt pads.

Heater assembly 100 is preferably insertable into a pocket 114 formedbetween wound tracing grid 86 and the barrier layer as discussed above.Finally, a temperature monitoring device, such as a liquid crystaltemperature monitor, may be applied to an upper surface of heaterassembly 100 or within treatment volume 112 to monitor the temperaturewithin treatment volume 112.

FIGS. 4-7 illustrate an alternate embodiment of wound covering 10. Inthis embodiment, wound covering 10 includes a generally circular head,designated generally at 12, which transitions to an elongatednon-kinking, collapsible air supply or hose 14.

The apparatus, as illustrated in FIG. 4, is connected by suitable supplyline or tube 16 to a source 18 of thermally controlled air which isschematically illustrated. The term air as used herein is intended toencompass mixtures of gases of controlled composition. The apparatus isconstructed to apply a continuous stream of thermally controlled air toa wound treatment volume.

The specific form of the apparatus and details of construction can bebest understood by reference to the various figures. The overallappearance of the wound covering is best seen in FIG. 4 and FIG. 5. Itis preferred to construct the apparatus from top and bottom sheets ofthin heat-sealable polymer film which overlay one another. A top sheetor membrane 20 overlies a bottom sheet or membrane 22 which are heatsealed together along a plurality of seal lines, including a continuousouter seam 24, which extends in a circle around head 12 and continues ina sinusoidal or convoluted fashion along and forming hose 14. An innercontinuous circular seal 26 is provided as best seen in FIGS. 6 and 7.This inner seam 26 secures the sheets together along a continuous circleto form the inner wall of a torus defining a supply volume 28.

The inner circular portion of the two sheets, 20, 22 in lying the planewithin the center of the supply volume 28 forms a wall 30 separating alower wound treatment volume 32 from an upper insulation chamber 34.Wall 30 includes a plurality of apertures 36 formed by making smallcircular seals 38 and cutting and removing circular portions within thecircular seals 38. Thus, wall 30, with a plurality of apertures 36, isformed between the wound treatment volume 32 and insulation chamber 34.A plurality of apertures 40 are formed in the common circular wallsurrounding treatment volume 32 for distributing and conveying heatedair or gases from supply volume 28 into wound treatment volume 32.

The heated air flowing into treatment volume 32 bathes the wound surfaceof a patient's body 42. The air circulates throughout wound treatmentvolume 32, and then passes through apertures 36 into the upper orinsulating chamber 34, when it then passes through a filter 44 formingan outer wall of insulation chamber 34. Filter 44 filters the airleaving wound treatment volume 32, trapping contaminants shed from thewound. Filter 44 may be constructed of a filter paper bonded along itsperiphery to the outer tangential walls of head 12 forming the torus.The filter paper also provides an insulating layer which suppresses lossof heat by radiation through upper wall 30.

The lower surface of the head 12 as shown in FIGS. 6 and 7 is providedwith a peripheral sealing ring 46 made of an absorbent material such asfoam and bonded by a suitable adhesive to the walls of head 12 and skin42 of the patient around the wound. Preferably, foam or cottonperipheral sealing ring 46 is provided with a peel-off tape so that itadheres to the wall of the hosing and on the other side to the skin ofthe patient. The adhesive or tape holds the apparatus in place andprevents airflow escape between the device and the skin of the patient.The absorbent material of the ring absorbs weeping blood and fluids andinsulates the skin from direct conduction of heat from head 12.

Hose 14 is designed to be non-kinking by forming it of symmetricallyconvoluted flexible material. The hose and housing are integrally formedessentially of a unitary structure, such as a thin film membrane. Hose14 is inflatable upon the application of heated air through supply line16. The indentations in hose 14 permit it to bend without kinking and,thus, differentiate from a straight tubular hose which may kink whenbent.

Since the thermal body treatment apparatus of the invention and thesupply hose section are formed from two, thin, sealed-togethermembranes, the hose, and in fact the entire apparatus, is collapsible.This prevents the possibility of applying heat and pressure to the skinas might happen if a patient rolled over on the device. Instead, theweight of the patient's body collapses the device, obstructing the flowof air, and preventing the application of heat.

The film membrane may preferably be transparent to enable viewing thewound without removal. However for cosmetic reasons the layer may beopaque. Filter paper 44 is attached across the tangential surfaces ofthe toroidal housing, thus providing a large area of filter for theescaping air. Head 12 of the apparatus may be about one foot in diameterfor most applications. However, it may be made smaller for certain otherapplications.

FIG. 8A illustrates an exploded view of an alternate embodiment of anon-contact wound covering 120 with climate control within a treatmentvolume 122 as shown in FIG. 8B. An inflatable structure 124 ispreferably attached to a fluid inlet line 126 at a fluid inlet port 129on the perimeter of inflatable structure 124. Inflatable structure 124is preferably attached to an absorbent peripheral sealing ring 128,which is in turn attached to a wound area 54 by a suitable adhesive 56.Peripheral sealing ring 128 preferably has a sealed outer surface and aporous inner surface which performs the same function as peripheralsealing ring 52 discussed above. A barrier layer 130 having an exhaustfilter 132 is attached to a top surface 134 on inflatable structure 124.

Turning now to the assembly illustrated in FIG. 8B, a gas, illustratedby direction arrows “A”, is introduced into inflatable structure 124from an external source (not shown) through inlet line 126. The gaspressurizes inflatable structure 124 in order to maintain barrier layer130 and exhaust filter 132 in an elevated position relative to woundarea 54. An inner surface 136 of inflatable structure 124 preferably hasa plurality of apertures 138 through which the fluid is introduced intowound treatment volume 122. As pressure within the treatment chamberincreases, excess pressure is relieved through exhaust filter 132. Inthis fashion, various fluids or gases can be introduced into woundtreatment volume 122.

The use of the term “fluid” in the context of this application refers toboth liquid and gaseous materials, and combinations thereof. In oneembodiment, oxygen may be introduced into treatment volume 122 throughapertures 138 of inflatable structure 124. The presence of oxygen withinwound treatment volume 122 may increase the oxygen available to thesuperficial layer of growing cells in wound area 54. Nitric oxidealternatively may be infused into treatment volume 122. Nitric oxide(NO) is a potent vasodilator which in theory may be absorbed across thewound surface and increase localized blood flow. A very smallconcentration of NO (parts per million) may provide this effect. NO mayalso be pre-absorbed into absorbent peripheral sealing ring 128 and thenallowed to passively diffuse into the volume once it is applied to thewound. Finally, gaseous or aerosolized medications or compounds may beintroduced into the gas flow entering treatment volume 122.

FIGS. 9A and 9B illustrate an alternate embodiment of the climatecontrol system discussed above wherein a fluid inlet line 140 may formpart of a barrier layer 142. Barrier layer 142 is unitary with the fluidinlet line 140 and is preferably attached to an exhaust filter media 144to allow excess pressure to be released from a wound treatment volume146. In this embodiment, filter media 144 forms part of barrier layer142. The arrows “A” in FIG. 9B illustrate the movement of the fluidthrough fluid inlet line 140, treatment volume 146, and exhaust filter144.

FIG. 10 illustrates an alternate embodiment wherein an exhaust filter154 is retained in a recess 150 formed in one side of a peripheralsealing ring 152. This structure allows excess fluid to be exhaustedthrough the side of peripheral sealing ring 152, rather than through thetop, as illustrated in FIGS. 9A and 9B.

FIG. 11A is a perspective view of the embodiment illustrated in FIG. 9A,wherein a connector 160 on the end of a fluid supply line 162 engageswith an opening 164 on fluid inlet line 140. FIG. 11B illustrates a sideview of fluid supply line 162 as it engages with the fluid inlet line140. FIG. 11C illustrates the embodiment in FIGS. 11A and 11B wherefluid inlet line 140 is folded over the top of peripheral sealing ring152 to seal treatment volume 146 when supply line 162 is uncoupled.

FIG. 12 illustrates an alternate embodiment in which a fluid inlet slot170 engages with a rigid connector 172 on a fluid inlet line 174. Fluidinlet slot 170 forms an opening in one portion of a peripheral sealingring 176. The opening is in fluid communication with a treatment volume178. This configuration allows for quick disconnection of fluid inletline 174 from wound covering 180 providing the patient with additionalmobility.

FIG. 13A is a perspective view of an alternate non-contact woundcovering 190 having a fluid inlet connector 192 attached to a topsurface 194 of a peripheral sealing ring 196. Fluid inlet connector 192preferably contains an inlet filter media 198. A rigid connector 200 ona fluid inlet line 202 mates with fluid inlet connector 192. Asillustrated in FIG. 13B, a cover 204 extends from the top of fluid inletconnector 192 across the top of peripheral sealing ring 196 where itengages with an exhaust filter media 206. FIG. 14 illustrates theembodiment of FIGS. 13A and 13B utilizing a non-disposable fluid supplyline 210.

FIG. 15 illustrates an alternate embodiment which utilizes a manifoldstructure 220 as part of a fluid inlet line 222 to provide evendistribution of the fluid being introduced into a treatment volume 224.Fluid inlet line 222 preferably has a series of seals 226 along its edgewhich are interrupted by a plurality of side openings 228 from which thefluid can be transmitted into treatment volume 224. The embodimentdisclosed in FIG. 15 illustrates an exhaust filter 230 recessed into theside of peripheral sealing ring 232. However, it will be understood thata variety of exhaust filter configurations are possible with thedisclosed manifold structure 220.

FIGS. 16A and 16B illustrate an alternate wound covering 240 with a topbarrier layer 242 and a lower layer 244 having a plurality of holes 246.As is illustrated in FIG. 16B, a top cover 243 forms the barrier layer242 and it extends substantially across the area of the peripheralsealing ring 248. Lower layer 244 likewise extends across the peripheralsealing ring 248. Thus, an upper insulating layer 250 is formed betweenlower layer 244 and the top of barrier layer 242. Fluid in a fluid inletline 252 is directed into upper insulating layer 250. The pressurizedfluid in upper insulating layer 250 passes through holes 246 into atreatment volume 254. Holes 246 in lower layer 244 provide a generallyeven distribution of the fluid within wound treatment volume 254. Anoptional seal 258 may be formed in the center portion of barrier layer242 and lower layer 244 to provide these layers with additionalstructural support. An exhaust filter medium 256 is provided in a recessalong one side of peripheral sealing ring 248 to relieve pressure intreatment volume 254.

FIG. 17 illustrates an alternate embodiment of a non-contact woundcovering 260 utilizing semi-rigid supports 262 to retain a barrier layer264 above a wound area. It will be understood by those skilled in theart that a variety of semi-rigid supports 262 may be utilized for thisapplication. For example, plastic or resilient rubber materials mayprovide sufficient support to barrier layer 264 with a minimum risk ofinjuring the patient.

FIGS. 18A and 18B illustrate an alternate exhaust filter medium 270 withan enlarged surface area to accommodate larger volumes of air flowthrough a non-contact wound covering 280. Exhaust filter 270 isincorporated into a fluid inlet line 272. Fluid inlet line 272 alsoforms a portion of a barrier layer 274, which is in turn attached to aperipheral sealing ring 276. As is best shown in FIG. 18B, fluidillustrated as the arrows “A” is introduced into a fluid inlet line 272,where it is directed into a wound treatment volume 278, past the woundarea and out through exhaust filter medium 270.

FIG. 19 illustrates a bi-directional line 290 with a center divider 292.Fluid is introduced into a fluid inlet line 294 where it proceedsthrough a fluid inlet port 296 into a treatment volume 298. The fluidthen is forced through a fluid outlet port 300 where it is driven awayfrom treatment volume 298 in a fluid outlet line 302. It will beunderstood by those skilled in the art that it would be possible toutilize separate fluid inlet and outlet lines to achieve the sameresult.

A schematic diagram of an embodiment of the present invention usingactive heating and control is depicted in FIG. 20 as an active heaterassembly 310 including a heater 312, a heater filament 314 within heater312, a controller 316, electrically coupled between heater filament 314and a power source 318 by electrical connectors 315, and using a heatertemperature sensor 320, and an operator interface 322 suitable for anoperator to input programming parameters into controller 316. Heaterassembly 310 is useful in several different configurations, for example,as providing a heater layer for use directly in a pocket such as thatdepicted by heater 100 inserted into pocket 114 shown in FIGS. 3A and 3Bor as a heat source for warming air that is circulated over the wound asis depicted in the several embodiments of FIGS. 4 through 19.

In addition to the various suggested fluid delivered heater “geometries”depicted in FIGS. 4-19, the present invention anticipates numerouspossible heater electrical resistive filament 314 geometries. Examplesof four such geometries are shown in FIGS. 21A, B, C, and D whereinthere is depicted additional alternate heater array geometries forheating filament 314 within heater 312. In FIG. 21A, there is depicted alinear geometry for heater filament 314. This geometry is suitable fornon-uniform heating where maximum heating is desired over a linear area,such as a linear surgical wound without direct heating over adjacentperiwound areas. FIG. 21B depicts a geometry for heater filament 314consistent more as a point source. FIG. 21C depicts an ovoid geometryfor filament 314 suitable for non-uniform heating of selected periwoundarea. Alternatively, this non-uniform heating may be achievable withcircular, square, rectangular, triangular or other such geometriesdepending on the type and shape of wound encountered.

In operation, heater assembly 310 is programmable, controlling severalparameters, such as heater temperature, duty cycle, therapy cycle,number of duty cycles per therapy cycle, average heater temperature perduty cycle, average heater temperature per therapy cycle, peak andminimum heater temperature per heater cycle, and peak and minimum heatertemperatures for a therapy cycle. The programming may be preset at timeof manufacture and may provide a menu of several treatment scenarios.Additionally, the parameter programmability may be entirely under thecontrol of an operator and suitable for inputting any number of customtreatment regimens.

By way of example, and not limiting in scope of treatment versatility,FIG. 22 is a graphic representation of one such therapy cyclerepresented by several heater and duty cycles. In FIG. 22, several dutycycles have been defined within a therapy cycle where time (t) isrepresented along the abscissa and heater temperature (T) along theordinate. At t₀ 330, the heater is at ambient temperature T_(amb) 332and the first of several duty cycles begins at t₀ 330 by turning on theheater to heat up to a temperature at about T_(peak) 334. Upon reachingT_(peak) 334 by t₁ 336, the heater power is turned off and the heatercools to T_(min) 338. The first duty cycle is completed at t₁ 336 whenthe heater is turned off. The first heater cycle is completed at t₂ 340when the heater is turned back on to begin the next duty and heatercycle. This first heater cycle and subsequent heater cycles maintain anaverage heater temperature T_(Dot) 342. The duty cycle is given by theratio of the duration of t₀-t₁ over t₀-t₂. Those familiar with the artof heater activity control will appreciate there are a variety ofmethods for manipulating heater activity, including proportional actioncontrollers using processor logic to maximize heater action and control.A therapy cycle for this example is the time duration from t₀ 330 to t₀344 during which time the heater temperature has been allowed to fall toT_(amb) 332, where at t₀ 344 the heating regimen begins again startingthe next therapy cycle.

For the above example, a peak temperature, T_(peak) 334 may be theparameter inputted into the program. For the present inventionanticipating a guard heater function, this range is preferably fromabove ambient to about 38° C. The present invention anticipatesalternative selections of temperatures inputted for the operatingtemperature. A first alternative is to establish an average heater cycletemperature. In FIG. 22, this concept is represented by T_(set) 342. Forthe present invention this average heater cycle temperature would havethe same range, from above ambient to about 38° C. Alternatively, thetemperature selection may be inputted as a T_(peak) 334 and a T_(min)338, both temperatures selected from the same range.

By way of another example, and not limiting in scope of treatmentversatility, a plurality of therapy cycles are depicted in FIG. 23,wherein individual heater cycles within each therapy cycle have beenaveraged out for purposes of clarification and for purposes herein aretreated as the heater being “on”. A first therapy cycle begins at t₀ 350as depicted by the heater turning “on”, i.e., a series of heater cyclesis begun, and the heater heats to T_(set) 352. This “on” segment goesuntil t₁ 354 at which time the heater is turned “off” and allowed tocool to T_(amb) 356. This first therapy cycle ends at t₂ 358 when asecond therapy cycle begins by turning “on” the heater again. As in thefirst therapy cycle, this second therapy cycle heats to T_(set) 352 andhas a duration from t₂ 358 to t₃ 360. A third therapy cycle begins at t₃360 turning “on” the heater. For purposes of example to depictanticipated versatility of the present invention, this third therapycycle is given a different T_(set) 362. The heater is turned “off” at t₄364. This entire period of multiple therapy cycles may also be part of atherapeutic sequence, depicted in FIG. 23 as that period of time from t₀350 to t₀ 366 encompassing three therapy cycles. The present inventionanticipates the use of any number of therapy cycles having any length orduration per cycle and different set temperatures.

Another aspect of heater therapy control is averaging the therapy cycleand therapeutic sequence temperatures, as depicted in FIG. 24. Theexample is not intended to be limiting in scope of treatmentversatility. In FIG. 24, a therapy cycle starts at t₀ 370 and ends at t₁372. The overall heater temperature average T_(ave) 374 for this therapycycle may be pre-selected or programmed. The heater, beginning at anyambient temperature T_(amb) 376, heats to an appropriate temperature forthe “on” phase and then is “off” for an additional appropriate time suchthat the total period of time is equivalent to the period t₀ 370 to t₁372 and the average temperature for this period is equivalent to T_(ave)374.

An alternative approach, also depicted in FIG. 24, anticipates theprogramming of a number of therapy cycles as elements of a therapeuticsequence, in this example there being three therapy cycles of varyingtime and heater temperature. The present invention versatility providesfor the inputting of an average temperature T_(ave) 378 for thetherapeutic sequence. The therapeutic sequence begins at time t₀ 370 andends at time t₀ 380. The heater temperatures and durations of thetherapy cycles within the therapeutic sequence are averaged by thecontroller over the entire period of time from t₀ 370 to t₀ 380 so as toachieve the therapeutic average temperature T_(ave) 378. Each of theseaverage temperatures, whether an average over a therapy cycle or over atherapeutic sequence, is intended to have the same temperature rangefrom above ambient to about 38° C. A secondary consequence of thiscontroller regimen is that if average temperatures are used, either overthe therapy cycle and/or therapeutic sequence, then the resultant peaktemperatures achieved by the heater may be substantially higher than theambient temperature to about 38° C. range. These peak temperatures areshort lived by comparison and do not represent a safety concern.

The present invention is the development of a safe, efficaciousnon-contact heater wound covering providing heat to a patient's woundfrom the heater that is in a temperature range from above ambient toabout 38° C. or controlled to an average temperature range from aboveambient to about 38° C. While the invention has been illustrated bymeans of specific embodiments and examples of use, it will be evident tothose skilled in the art that many variations and modifications may bemade therein without deviating from the scope and spirit of theinvention. However, it is to be understood that the scope of the presentinvention is to be limited only by the appended claims.

TABLE 1 Time Subcutaneous Temperature (in minutes) (° C. mean ± S.D.)−60 33.8 ± 1.7 0 34.4 ± 1.3 30 36.1 ± 0.9 60 36.4 ± 0.8 90 36.6 ± 0.7120 36.9 ± 0.6 180 35.8 ± 0.6 240 35.9 ± 0.5 300 35.6 ± 0.6

TABLE 2 Time Skin Temperature Inside Covering (in minutes) (° C. mean ±S.D.) −60 32.9 ± 1.4 0 33.5 ± 1.0 30 35.8 ± 0.8 60 36.2 ± 0.6 90 36.2 ±0.6 120 36.4 ± 0.5 180 34.9 ± 0.5 240 34.9 ± 0.4 300 34.9 ± 0.6

TABLE 3 Time Laser Doppler Flow (in minutes) (ml/100 g/min mean ± S.D.)−60 49 ± 31 0 74 ± 65 30 83 ± 75 60 199 ± 262 90 132 ± 127 120 110 ± 116180 89 ± 73 240 76 ± 65 300 71 ± 53

TABLE 4 Time Subcutaneous Oxygen Tension (P_(aq)O₂) (in minutes) (mm Hgmean ± S.D.) −60  55 ± 9  0  81 ± 26 30  90 ± 32 60 112 ± 56 120 134 ±74 180 126 ± 65 240 129 ± 49 300 131 ± 52

What is claimed:
 1. A covering for application to a tissue treatmentarea of a patient's body, said wound covering comprising: a heatersuitable for providing heat to the tissue treatment area; flexibleattachment means for attaching the heater in a non-contact positionproximate the tissue treatment area; and a controller connected to theheater for controlling the temperature of the heater in a temperaturerange from ambient temperature to 38° C.
 2. An apparatus for treatingtissue on a patient's body, the apparatus comprising: a flexiblematerial having an upper and lower surface and an opening; a layerspanning the upper surface, over the opening; an attachment portionproximate the lower surface; and a heater supported by the layer, overthe opening, for maintaining a tissue treatment temperature in a rangefrom ambient to 38° C.
 3. The apparatus of claim 2, wherein the openingextends from the first surface to the second surface.
 4. The apparatusof claim 2, in which the heater is an active heater.
 5. The apparatus ofclaim 2, in which the heater is a heat reflective layer.
 6. Theapparatus of claim 2, in which the heater is selected from the groupcontaining warm water pads, chemical heating pads, and phase-change saltpads.
 7. The apparatus of claim 2, further including a controllerconnected to the heater for causing the heater to maintain the tissuetreatment temperature in the range.
 8. The apparatus of claim 7, inwhich the heater is an active heater.
 9. The apparatus of claim 8, whichthe heater is an electrical heater.
 10. The apparatus of claim 2,further including means on the layer for receiving the heater.
 11. Theapparatus of claim 2, in which the flexible material forms a ring. 12.The apparatus of claim 11, in which the ring is a sealing ring.